Drift tube for klystron



Nm NIH `Filed July 20. 1954 TTOP/VE Y .shaped' anodel, say of copper.

drift: tube section 4 at braze 141and has an aperture 15;

United States Patent O 2,824,289 DRIFT TUBE non KLYsrRoN My invention relates to ldystrons having'r cavity reso-` nators, and more particularly to such klys'tronsfin 'which theresonators have portions forming part ofthe evacuated envelope and'separated from external resonator portions byV vacuum-tightinsulating walls. H i

It is among the objectsl of my'inventionto provide al klystron of the character described which is madeA up of a series of` structural units or subasseniblies"separatelyl fabricated and later joined at vseals spaced'along the *axisv ofthe envelope. v v v Another object is to provide improvements in the resonatorf` structures which form part'of the evacuated en*y velope.

Another object is to provide animproved joint struc-l ture` between resonatorend walls and a ceramiccylinderf which comprises the insulating wall member. l

Stillanother object is to provide such a structure wherein the,v iinal seals are made at the above mentioned joints afterthe subassemblies have been completed. Y

A further object is tol provide an improved-method of assemblying the klystron.

The'invention possesses other objects andfeatures of advantage, some of which, with the foregoing, will be set forthfin'lthe following description of my invention. It is to'be understood that I do not limit myself-to thisrdis-v closure of species of my invention, as I may adopt variant embodiments thereof within the scope ofthe claims.

` Referring to the drawing:

Figure l is an axialsectional View of ya three-cavity klystron embodying my invention; and

Figure Zisan exploded view showing the subassemblies prior Vto making vthe iinalseals.

` In its preferredform as illustrated in Figure 1, my improved lklystron comprises an elongated generally cylindricalevacuated envelopehaving an electron ,gun assembly 2y atione endl and a collector electrode assembly Slat the other end. The electron beam from the gun to Athepcollec-v tor vpasses through a drift tube made up of sections 4,l 6,V 7,v and 8` ofa metal such as copper extending axially off the envelope and having gaps 9 therebetween. The gaps arel bridged by cavity resonators generally designated at 11.

Electron gun 2 comprises a cathode 12-housed in a cup- The anode is xedtto ahead of the cathode and opening .into the di'iftvtube.y

Electrons from lthe'cathode are focusedthroughl theanode aperture by a focusing electrode 16. Theentire' gun structure'is mounted on a suitable stem 17 at the endof the envelope, which stern may be of conventional glass and metal construction and providing suitablek terminals for the cathode. i

The gun structure of my improved klystron comprises a unitary subasseniblyv which may, be .Separately fabricated as shown in Figure 2. Gunassemblyrll isrsealed to anode 13 at a joint comprising a pair -of nested metal flanges 18 and 19;; on` the stein Vand yanode respectively, ilange, 18 being. Sealedfto a glassy/ al1 of therstemi and aangaw lice 2 beingbrazed at 2,0 to the end of anode 13. These ringshaped flanges are concentric with the envelope axis and when itted together are weldedalong the registering edges at 21 to provide a vacuum-tight sealV at this joint.

Collector assembly 3 at the opposite end of the envelope comprises a cup-shaped collector electrode 212, say of copper, connected to drift tube section 8 at braze 24'. Collector electrode' 22 also preferably carries a metall exhaust tubulation 25 which is pinched oif at 26 after evacuation of the envelope. The collector may be cooled by a suitable water jacket 21 or the like.

The collector structure thusalso comprises a unitary subas'sembly which may be separately fabricated as shownk inL Figure 2 This collector assembly, including the last drift tube section 8, is sealed` atl a joint structure which comprises part of the thirdcavity resonator, hereinafterdescribed;

The above elementsofA the electron tube function in the conventional manner for klystron tubes of this type, nainely, the electron beam from cathode 17,2 is accelerated by apositive potential on anode 13 and passes throughthe drift tube, past the interaction spaces provided by gaps 9, and finally terminates at collector electrode 22;. The three cavity 'resonators 11-l coacting with the interaction spaces provided by gaps 9 serve as the frequency determining e1ements of the device. In the three-cavity klystron illustrated, functioning as an amplifier, the radio-frequency input is fed into the lrstresonator andrthe output is taken from the third-resonator.

In the particular kindof1 klystron shown in Figure l the cavity resonators llhave extensions 23 externally ofL the'evacuated envelope to permit external tuning. These extensions, one of vwhich is indicated by dotted lines in Figure l, may simply comprise split rectangular metal boxesffastenedto the resonators 1l,` which boxes contain suitable sliding end walls for changing the resonant frequency of the resonators. The use of such external resonator construction, which permits tuning over a wide frequency range, is made possible becausey vof the sealed-olfnature of resonators ll-which comprise part of the evacuated envelope.

Resonators 11( are mounted on drift tube sections 4,

6, 7, and 8 to bridge gaps 9; Itis thus seen that the drift tube sectionsV form side walls of the evacuatedenvelope axially of the klystron andthatfthe resonator structures provide additional vacuum-tight walls bridging the gaps between the drift tubeV sections. The resonators are of like construction, each comprising a pairjof metal end wall disks 29 connected by a cylindrical insulatingy wall 3i. Walls 29, preferably of copper, are apertured to receive the `drift tube sections and are fixedto the latter at brazes 30:

TheV nal seals are made atjoint structures between the resonator endwalls 29 and the interposed insulating cylinders 31 so that the klystron is divided into structural units or subassemblies axially along the envelope, as best shown by the exploded VView4 of `Figure 2. Thus anode 13, drift tube section 4, and an endvwall 29 can be as sembled and brazed together as a unitfin abrazing furnace. Likewise, drift tube Section 6 with another pais' of end walls 29fforms another subassembly, and similarly drift tube section 7 :with another pair of end wallsforms still anothersubassembly. Ina like manner the collector structure oni-drift tubesection; which also carriesanv end wall:29;.makes up a .further subassembly.

ceramic used is preferably a type having good mechanical and insulating properties, such as alumina, and is metalized at the ends by any of the conventional metalizing techniques so that flanges 32 can be applied.

I prefer to make flanges 32 cup-shaped so that the inturned portions overlap the ilat ends `of cylinders 31, which overlapping portionsare bonded tothe metalized ends of the ceramic at brazes 34. Flanges 33 are simple ring-shaped pieces projecting from the end plates and secured thereto at brazes 35. These flanges 32 and 33 are thus arranged concentric with the envelope axis 37 and when finally tted together are sealed along the registering edges at 36 to provide vacuum-tight joints. Seals 36 are preferably fused metallic bonds, such as welds. It is thus seen that the subassemblies may be slipped together axially and then sealed by welding the flanges.

End walls 29 are preferably undercut at the joints to provide clearance under iianges 32. In order to take the axial thrust of atmospheric pressure, I leave a narrow spacer ring 38 projecting from the end wall and abutting the end of the cylindrical wall structure. This relieves the sealing flanges from stress after the envelope is evacuated and allows the anges to be made of relatively thin material which is desirable to give some degree of flexibility at the joints.

The relationship between the several structural units prior to final sealing is clearly shown in Figure 2. Ability to fabricate the envelope in separate subassemblies is important in a kylstron of this kind where appreciable length and relatively `massive parts are involved. For example, in a power klystron capable of delivering, say, ten kilowatts of C. W. power in the UHF region, the tube is several feet long and weighs titty pounds or so. With my improved construction, the subassemblies are each relatively small and can be put together and brazed in a furnace of convenient size.

It will be noted that the final sealing flanges are all concentric with the tube axis, so that when the subassemblies are put together they may be rotated about the axis during the final welding operations. Welding of the tianges is done with a heli-arc which involves keeping the arc fixed while rotating the work about an axis. v

Another important feature of my construction and method of assembly is that the ceramic wall sections, after application of the end flanges 32, do not have to be subjected to additional brazing furnace temperatures. Additional high temperature heat cycling of the flanged ceramic sections is bad because of weakening of the bonds at the metalized areas. The only thing that the anged ceramic sections are further subjected to in my structure is the heli-arc welding at the iiangesg which is a localized heating operation and does not subject the metalized areas to injury.

Still another feature which facilitates the assembly procedure is that sealing flanges 32 and 33 are concentric with the axis 37 and hence serve as self-jigging devices to insure coaxial alignment of the parts. This is particularly important in a klystron wherein alignment of the drift tube sections must be held to close tolerances to insure optimum performance.

The several advantages come about by reason of the improved structure and method of assembly, namely, by fabricating the envelope in a series of separate structurally integral -units coaxially aligned along the envelope axis, which subassemblies are joined together at the engaged anges 32 and 33 having registering edges lying in parallel planes disposed perpendicular to the envelope axis. This structure allows the coaxial metal anges to be telescoped together by relative movement of the subassemblies axially of the envelope and permits rotating the engaged subassernblies about the common axis so that the sealing operation can be easily accomplished by welding the registering edges of the rotating tianges.

I claim:

1. In a klystron having a drift tube including a series lll of metal sections with gaps therebetween, a plurality of resonators each including a pair of metal end walls and an insulating cylinder therebetween, the several pairs of end walls each being fixed to the drift tube sections at opposite sides of a different one of said gaps so that two walls of adjacent resonators together with an interconnecting drift tube section form a structurally integral unit, the improvement comprising a ring-shaped metal flange fixed to each end wall and being in an overlapping externally concentric relationship with respect to the associated insulating cylinder, a cup-shaped ring-like metal end liange iixed to each insulating cylinder and being in an overlapping externally concentric relationship with respect to the associated insulating cylinder and nesting closely within the associated ring-shaped metal ange supported on the adjacent end wall with the edges of said ring-shaped flange and cup-shaped flange in registration, fused metallic bonds uniting the registering and nested edges of the engaged lianges, and a spacer ring supported on each end wall and axially aligned in crosssection with the length of the associated cylinder wall and mechanically coupled to the associated end of the insulating cylinder.

2. In a klystron having a drift tube including a series of metal sections with gaps therebetween, a plurality of resonators each including a pair of metal end walls and an insulating cylinder therebetween, the several pairs of end walls being ixed to the drift tube sections at opposite sides of a different one of said gaps so that two walls of adjacent resonators together with an interconnecting drift tube section form a structurally integral unit, the improvement comprising a ring-shaped metal ange tixed to each end wall and being in an overlapping externally concentric relationship with respect to the associated insulating cylinder, a cup-shaped ring-like metal end ange fixed to each insulating cylinder and being in an overlapping externally concentric relationship with respect to the associated insulating cylinder and nesting closely within the associated ring-shaped metal flange supported on the adjacent end wall with the edges of said ring-shaped flange and cup-shaped flange in registration, fused metallic bonds uniting the registering and nested edges of the engaged flanges, and projecting means supported on each end wall and aligned in `cross-section with the length of the associated cylinder wall and mechanically coupled to the associated end of the insulating cylinder.

3. In a klystron having a drift tube including a series of metal sections with gaps therebetween, a plurality of resonators each including a pair of metal end walls and an insulating cylinder therebetween, the several pairs of end walls being fixed to the drift tube sections at opposite sides of a different one of said gaps so that two walls of adjacent resonators together with an interconnecting drift tube section form a structurally integral unit, the improvement comprising a first metal flange fixed to cach end wall and being in an overlapping externally concentric relationship with respect to the associated insulating cylinder, a second metal end llange fixed to each insulating cylinder and being in an overlapping externally concentric relationship with respect to the associated insulating cylinder and nesting closely within the associated first metal ange supported on the adjacent end wall with the edges of said tirst and second metal tianges in registration, fused metallic bonds Limiting the registering and nested edges of the engaged flanges, and a spacer supported on each end wall and aligned in cross-section with and mechanically coupled to the associated end of the insulating cylinder.

References Cited in the tile of this patent UNITED STATES PATENTS 

